Duplicate UUID if we enter a new input from html? - django

Question

getting error- i saved one form from html into my database
while when i tried saving the next it gave me this error-
IntegrityError at customer
(1062, "Duplicate entry 'ad138e46-edc0-11va-b065-a41g7252ecb4'' for key 'customer.PRIMARY'")
kindly explain my uuid in models.py is -
class customer(models.Model):
customerid = models.CharField(default=str(uuid.uuid4()), max_length=500, primary_key=True)
customername=models.CharField(max_length=100)
kindly help
Updated
Form.py
class createcustomerform(ModelForm):
class Meta:
model=customer
fields=[
'customername']
Updated Models.py
import uuid
from uuid import UUID
from django.contrib.auth.models import User
from django.dispatch.dispatcher import receiver
from django.utils.translation import ugettext_lazy as _
from django.db.models.signals import pre_save
class customer(UUIDMixin,models.Model):
customername=models.CharField(max_length=100)
def __str__(self):
return self.customername
class UUIDMixin(models.Model):
uuid = models.UUIDField(blank=True,db_index=True,default=None,help_text=_('Unique identifier'),max_length=255,null=True,unique=True,verbose_name=_('UUID'))
class Meta:
abstract = True
#classmethod
def check_uuid_exists(cls, _uuid):
#Determine whether UUID exists """
manager = getattr(cls, '_default_manager')
return manager.filter(uuid=_uuid).exists()
#classmethod
def get_available_uuid(cls):
#Return an Available UUID """
row_uuid = uuid.uuid4()
while cls.check_uuid_exists(uuid=row_uuid):
row_uuid = uuid.uuid4()
return row_uuid
#receiver(pre_save)
def uuid_mixin_pre_save(sender, instance, **kwargs):
if issubclass(sender, UUIDMixin):
if not instance.uuid:
manager = getattr(instance.__class__, '_default_manager')
use_uuid = uuid.uuid4()
while manager.filter(uuid=use_uuid):
use_uuid = uuid.uuid4()
instance.uuid = use_uuid
#Automatically populate the uuid field of UUIDMixin models if not already populated.

Answer 1

You should use a proper UUIDField and avoid setting a default value.
Make sure the value is set when the object is created, and also ensure that the value is unique - obviously the chance of duplication in a UUID is incredibly small which is the whole point.
You could create yourself a model mixin which will add a uuid to your model(s) and ensure that the value is set when the object is saved;
class UUIDMixin(models.Model):
"""
Mixin for models contain a unique UUID, gets auto-populated on save
"""
uuid = models.UUIDField(
blank=True,
db_index=True,
# default=uuid.uuid4,
# NB: default is set to None in migration to avoid duplications
default=None,
help_text=_('Unique identifier'),
max_length=255,
null=True,
unique=True,
verbose_name=_('UUID'),
)
class Meta:
"""Metadata for the UUIDMixin class"""
abstract = True
#classmethod
def check_uuid_exists(cls, _uuid):
""" Determine whether UUID exists """
manager = getattr(cls, '_default_manager')
return manager.filter(uuid=_uuid).exists()
#classmethod
def get_available_uuid(cls):
""" Return an Available UUID """
row_uuid = uuid.uuid4()
while cls.check_uuid_exists(uuid=row_uuid):
row_uuid = uuid.uuid4()
return row_uuid
#receiver(pre_save)
def uuid_mixin_pre_save(sender, instance, **kwargs):
"""
Automatically populate the uuid field of UUIDMixin models if not already
populated.
"""
if issubclass(sender, UUIDMixin):
if not instance.uuid:
manager = getattr(instance.__class__, '_default_manager')
use_uuid = uuid.uuid4()
while manager.filter(uuid=use_uuid):
use_uuid = uuid.uuid4()
instance.uuid = use_uuid
Based on your comment, let me explain more.
The above is an abstract model, meaning it doesn't create a table itself, it can just be used by other (concrete) models so that they can use what it defines.
It's a benefit of classes & inheritance. Allowing you to not duplicate code on things that will be useful on many models.
No, in the meta you'll see abstract = True. So you define your models like MyModel(UUIDMixin, models.Model) and it gets a uuid field from this abstract model along with whatever you define.
You would use it by doing something like this;
class Customer(UUIDMixin, models.Model):
name = models.CharField(max_length=100)
If you really want to use the UUID as a primary key, maybe setup two mixins, a PrimaryUUIDMixin and the UUIDMixin, because on the whole a smaller value on the primary key may be more efficient.
You also mentioned Undefined variable: _
Typically in django you'd see an import at the top of the file like this;
from django.utils.translation import ugettext_lazy as _
This is then used to wrap strings so that they can be translated, for example, _("Hello")
Even if you don't translate your project, it's common to just include this anyway. You can read up on that here; https://docs.djangoproject.com/en/3.1/topics/i18n/translation/#standard-translation